At present, in the field of wireless network, WLAN develops rapidly, the needs and requirements on the coverage of the WLAN are increasing, and the requirements on the throughput are also increasing. In group IEEE802.11 of the industrial specification of the Institute of Electrical and Electronic Engineers, most common WLAN technologies of a series of standards such as 802.11a, 802.11b, 802.11g etc. are defined successfully, and then other task groups appear in succession, which devote themselves to the development of specifications involving improvements of existing 802.11 technologies, for example, the 802.11n task group proposes the requirements on High Throughput (HT) to support a data rate up to 600Mbps; and the 802.11ac task group further proposes a concept of Very High throughput (VHT), which increases the data rate to 1Gbps by introducing a larger channel bandwidth. The new protocol needs backward compatibility with the former protocols.
In 802.11, one Access Point (AP) and multiple Stations (STAs) associated with the AP constitute one Basic Service Set (BTS). The 802.11 defines two kinds of operation modes, which are Distributed Coordination Function (DCF) and Point Coordination Function (PCF), and improvement modes for the two operation modes, which are Enhanced Distributed Channel Access (EDCA) and Hybrid Coordination Function Controlled Channel Access (HCCA). Wherein, the DCF is a most basic operation mode, which takes use of the CSMA with Collision Avoidance (CSMA/CA) mechanism to make multiple STAs share a wireless channel. The EDCA is an enhanced operation mode, which uses the CSMA/CA mechanism to make multiple queues of different priorities share a wireless channel and can subscribe one Transmission Opportunity (TXOP).
When multiple wireless STAs share a wireless channel for data transmission, the collision detection for the wireless environment becomes very difficult, one large problem of which is hidden STAs, as shown in FIG. 1. STA A transmits data to STA B, and meanwhile, STA C also transmits data to STA B. As both the STA C and the STA A are located in the coverage of each other, transmitting data by the STA A and the STA C at the same time will lead to collision. From the point of view of the STA A, the STA C is a hidden STA, vice versa.
In order to solve the problem of hidden STAs, 802.11 proposes a virtual channel detection mechanism, i.e., when the transmitting STA and the receiving STA perform channel subscription, time information of the subscribed channel is included in the frame header of the radio frame, for example, when the transmitting STA transmits a Request to send (RTS) including the time information of the subscribed channel for channel subscription, and the receiving STA transmits a Clear to send (CTS) which also includes time information of the subscribed channel to acknowledge the channel subscription, to ensure that the transmitting party can complete the frame exchange. After receiving the radio frame including the time information of the subscribed channel, other visiting STAs set a value of a Network Allocation Vector (NAV) which is stored locally as a maximum of the above time information of the subscribed channel. Within the NAV time, the other visiting STAs will not transmit data, thus avoiding the hidden node from competing for channels, which causes collision. Only after the NAV time reduces to zero, the other visiting STAs will transmit data. The method of using the RTS/CTS frames is shown in FIG. 2.
The above RTS/CTS mechanism is primarily applied to a traditional channel bandwidth of 20 MHz. With the evolution of the 802.11 protocol, the traditional channel bandwidth of 20 MHz has gradually been extended to large bandwidth channels of 40 MHz, 80 MHz, 120 MHz, and even 160 MHz, and these large bandwidth channels are formed by binding several 20 MHz, wherein, one 20 MHz is referred to as a primary channel or the first channel, and other channels of 20 MHz are referred to as auxiliary channels or the second channel, the third channel, and so on. On a frequency spectrum of 5 GHz, the large bandwidth channel is typically comprised of non-overlapping channels of 20 MHz, and according to a channelization principle, the bandwidth of 160M therein is comprised of two adjacent or non-adjacent bandwidths of 80M, and each bandwidth of 80M is comprised of two adjacent channels of 40 MHz, and is not overlapped with other bandwidths. Each bandwidth of 40M is comprised of two adjacent basic bandwidth channels of 20 MHz, and is not overlapped with other bandwidths. The bandwidth formed by such a channelization mode is referred to as a channelization bandwidth. The composition example of various different channelization bandwidths in the large bandwidth system is shown in FIG. 3.
Presently, the traditional 802.11 device is applied extremely widely, and these traditional BSSs are very likely to be overlapped with the next generation of large bandwidth BSS in terms of coverage. Thus, there will be multiple overlapping BSSs (OBSSs) operating on the same or different channel bandwidths within the same segment of frequency spectrum, thus forming potential interference on the channel with each other. When a large bandwidth is to be used for transmission between the AP and the STA, it is needed to ensure that all the channels which are used by them be in an idle state. However, as there is a number of traditional BSSs, the probability for the large bandwidth BSS to use the maximum bandwidth for transmission is indeed very low, and the probability for collision increases, which leads to a decrease of the efficiency of the large bandwidth transmission.
Therefore, how to efficiently perform data transmission on the large bandwidth and enhance the average effective bandwidth of the system is a problem to be solved in the new generation of 802.11 protocols based on large bandwidths.